Security forces opened fire on demonstrators in Syria's third largest city after thousands vowed to occupy the main square until the overthrow of President Bashar al-Assad, witnesses said.
The government, which has failed to quell intensifying protests with promises of reform and an end to emergency rule, blamed Muslim extremists for what it called an "insurrection."
Witnesses said at least one protester was hurt by gunfire in Al Saa (Clock) Square in Homs, where thousands were mourning people killed in earlier protests, Reuters said. Tear gas was also used.
Al Jazeera said security forces imposed checkpoints across Homs as they tried to shut down the city.
The protests were the latest in a month of anti-government unrest that have prompted a deadly crackdown by security forces resulting in the death of at least 200 people, according to human rights groups.
Assad on Saturday promised a series of reforms and an end to nearly half-a-century of emergency rule in an apparently futile effort to appease the demonstrators.
In a statement on Monday, Syria's Interior Ministry blamed the turmoil on ultra-conservative Salafist Muslims -- who some Arab governments equate with Al Qaeda extremists.
"The latest incidents have shown that... armed Salafist groups, particularly in the cities of Homs and Banias, have openly called for armed revolt," it said.
Authorities "will act with determination to impose security" and will "pursue the terrorists wherever they are in order to bring them to justice and end the armed revolt," it added.
Activists meanwhile set up tents in Clock Square, hoping to emulate the occupation of central Cairo's Tahrir Square during the movement that toppled Egypt's Hosni Mubarak in February.
"More than 20,000 people are taking part in the sit-in at Al-Saa Square (Clock Square) and we have renamed it Tahrir Square like the one in Cairo," rights activist Najati Tayyara told AFP.
"It is an open-ended sit-in which will continue until all our demands are satisfied," Tayyara said.
"This despotic regime must change. We have been waiting for 11 years for reforms," said Tayyara of the 11-year rule of Assad, who succeeded his autocratic father Hafez following his death in 2000.
"The young people are ready to face anything, including martyrdom."